Splits feature flag for removing note attributes

What does this MR do and why?

The original feature flag to remove user attributes !96447 (merged) was only scoped to groups, which meant that the attributes would only be removed on epics, but not on issues, merge requests or incidents. We are now instead splitting up the feature flag into one for groups, and one for projects.

Screenshots or screen recordings

Before	After

How to set up and validate locally

For groups, enable remove_user_attributes_groups. For projects, enable remove_user_attributes_projects.

MR acceptance checklist

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